The present invention relates to an accumulator for forming a refrigerating and air-conditioning circuit for use in an air conditioning machine or a refrigerator.
A conventional accumulator for forming a refrigerating and air-conditioning circuit by using, for example, a refrigerant, for example, refrigerant R22, and mineral oil (refrigerating machine oil) having mutual solubility will now be described.
FIG. 31 is a vertical cross sectional view showing the structure of a representative accumulator disclosed in a document ("Closed Compressor" written by Mutsuyoshi Kawahira, Issued by Japan Refrigeration Association, Jul. 30, 1981).
Referring to the drawing, reference numeral 151 represents a container, 152 represents a suction pipe, 153 represents a discharge pipe and 153a represents an oil-recovery hole formed in the bottom portion of the discharge pipe 153. Reference numeral 153b represents a discharge-pipe inlet opening formed at an end of the discharge pipe 153. Reference numeral 154 represents a liquid refrigerant (in a state in which refrigerating machine oil is dissolved) having a soluble relationship with refrigerating machine oil which is accumulated in the container 151. Reference numeral 155 represents a gas refrigerant.
The operation of the foregoing accumulator will now be described. In a refrigerating and air-conditioning circuit including the accumulator, the gas refrigerant 155 and the liquid refrigerant (including refrigerating machine oil) 154 flow through the suction pipe 152, and then introduced into the container 151 as indicated by an arrow A. In the internal space of the container 151, the refrigerant gas and the liquid refrigerant (including refrigerating machine oil) 154 are subjected to a process for separating the gas and the liquid from each other. Then, the gas refrigerant 155 is allowed to flow from the discharge-pipe inlet opening 153b to pass the discharge pipe 153, and then discharged to the outside of the container 151. On the other hand, the liquid refrigerant (including refrigerating machine oil) 154 is accumulated in the lower portion of the container 151. Then, refrigerating machine oil dissolved in the liquid refrigerant (including refrigerating machine oil) 154 is allowed to pass through the oil-recovery hole 153a and, together with the gas refrigerant 155 and the liquid refrigerant (including refrigerating machine oil) 154, allowed to flow to a compressor as indicated by an arrow B. The size of the oil-recovery hole 153a is determined to enable recovery of refrigerating machine oil to reliably be performed.
Problems experienced with the conventional accumulator shown in FIG. 31 will now be described.
When the refrigerating and air-conditioning circuit is operated, a state is realized in which the liquid refrigerant (including refrigerating machine oil) 154 is accumulated in the container 151 as shown in FIG. 31 depending upon a state of the operation.
The flow rate of the liquid refrigerant (including refrigerating machine oil) 154 which flows from the oil-recovery hole 153a into the discharge pipe 153 is enlarged as the flow velocity of the gas which flows in the discharge pipe 153 is raised and as the quantity of the liquid refrigerant which is accumulated in the container 151 is enlarged, that is, as the height H of the liquid refrigerant is enlarged. The characteristic of the flow rate realized when the velocity of the gas is made to be constant is shown in FIG. 32.
In the drawing, the axis of abscissa stands for the height H (mm) of the liquid refrigerant and axis of ordinate stands for the flow rate (kg/h) of the liquid refrigerant (including refrigerating machine oil) 154 which is introduced from the oil-recovery hole 153a into the discharge pipe 153. The rate of the flow from the oil-recovery hole 153a is a value obtained by adding a flow rate, which is substantially proportional to the square root of the height H (mm) of the liquid refrigerant, to a substantially constant flow rate. Note that the height H of the liquid refrigerant is a height from the oil-recovery hole 153a to the liquid refrigerant 154.
It is a known fact that the gas refrigerant discharged from the discharge pipe of the accumulator is, in the refrigerating and air-conditioning circuit, sucked by the compressor. Then, the gas refrigerant is compressed, and then discharged. The accumulator having the conventional structure encounters a phenomenon that the flow rate of the liquid refrigerant which is introduced into the discharge pipe 153 of the accumulator is enlarged excessively if the liquid refrigerant 154 in a large quantity is accumulated in the container 151. At this time, the compressor is brought to a state which sucks the liquid refrigerant in a large quantity. As a result, a state in which the liquid refrigerant is compressed is realized, causing an abnormally high pressure to be generated. Also the inside portion of the compressor encounters defective lubrication of the bearing portions because an oil-supply pump sucks the liquid refrigerant and thus supplies the liquid refrigerant to the bearing portions and sliding portions. As a result, mechanisms in the compressor will be broken, and abnormal abrasion and seizure of the sliding portions in the compressor take place.
The characteristic of a flow in an accumulator for a refrigerating and air-conditioning circuit in which refrigerating machine oil having no solubility with the refrigerant is employed and problems which arises in this case will now be described.
Another example of the conventional accumulator will now be described. FIG. 33 is a vertical cross sectional view showing the structure of an accumulator disclosed in Japanese Patent Publication No. 5-39409.
Referring to the drawing, reference numeral 201 represents a container, 202 represents a suction pipe, 203 represents a discharge pipe and 204 represents liquid refrigerant accumulated in the container 201. Reference numeral 205 represents refrigerating machine oil. Reference numeral 203a to 203e represent plural oil recovery holes opened in the vertical direction of the discharge pipe 203. In this example, five oil recovery holes are formed. Reference numeral 203f represents a gas inlet port formed at an end of the discharge pipe 203. Symbol U indicates the velocity of a gas in the discharge pipe 203.
In the refrigerating and air-conditioning circuit including the foregoing accumulator, a fluid containing a gas refrigerant, a liquid refrigerant and refrigerating machine oil is allowed to pass through the suction pipe 202, and then introduced into the container 201. The gas refrigerant and the liquid refrigerant are separated from each other in the internal space in the container 201. Then, the gas refrigerant is allowed to flow from the gas inlet opening 203f to pass through the discharge pipe 203, and then discharged to the outside of the container 201. On the other hand, the liquid refrigerant 204 and refrigerating machine oil 205 are accumulated in a lower portion of the container 201.
If refrigerating machine oil 205 has poor or no solubility with the liquid refrigerant 204 or if refrigerating machine oil 205 encounters phase separation from that of the liquid refrigerant 204 depending on the operating condition, refrigerating machine oil 205 and the liquid refrigerant 204 in the container 201 are separated from each other as shown in the drawing. As a result, refrigerating machine oil 205 having a thickness h floats on the liquid refrigerant 204 having the liquid level of H. The plural oil-recovery holes 203a to 203e are formed in the vertical direction so that refrigerating machine oil 205 and the liquid refrigerant 204 are sucked into the discharge pipe 203 through the oil-recovery holes 203a to 203e. Thus, they are mixed with the gas refrigerant and allowed to flow in the apparatus.
Another example of the conventional accumulator will now be described. FIG. 34 is a vertical cross sectional view showing the structure of an accumulator disclosed in Japanese Utility-Model Laid-Open No. 58-87079. The internal structure of the accumulator is different from that of the conventional apparatus shown in FIG. 33.
Referring to the drawing, reference numeral 206 represents a container, 207 represents a suction pipe and 208 represents a discharge pipe. Reference numeral 208a to 208e represent a plurality of oil-recovery holes vertically formed in the discharge pipe 208. Reference numeral 209 represents a liquid refrigerant and 210 represents refrigerating machine oil.
In the refrigerating and air-conditioning circuit including the above-mentioned accumulator, a fluid containing the gas refrigerant, the liquid refrigerant and refrigerating machine oil is allowed to pass through the suction pipe 207, and then introduced into the container 206. In the internal space in the container 206, the gas refrigerant and the liquid refrigerant are separated from each other. Moreover, refrigerating machine oil 210 and the liquid refrigerant 209 are separated from each other. Refrigerating machine oil 210 having a low specific gravity is brought to a state in which it floats on the liquid refrigerant 209. Since the plural oil-recovery holes 208a to 208e are formed vertically, refrigerating machine oil 210 and the liquid refrigerant 209 are sucked into the discharge pipe 208 through the oil-recovery holes 208a to 208e. Then, they are mixed with the gas refrigerant, and allowed to flow in the apparatus.
The two conventional structures are operated similarly and suffers from similar problems. The operation and problem of the conventional structure shown in FIG. 33 will now be described.
The flow rate of the liquid refrigerant which is introduced into the discharge pipe 203 through the oil-recovery holes 203a to 203e is enlarged as the velocity U of the gas which flows in the discharge pipe 203 is raised and the quantity of the liquid refrigerant which is accumulated in the container 201, that is, the height H of the liquid refrigerant, is enlarged. FIG. 35 shows a flow-rate characteristic realized on the assumption that the gas velocity U is a constant value and the thickness h of refrigerating machine oil 205 which floats on the liquid refrigerant 204 is constant.
Referring to FIG. 35, the axis of abscissa stands for the height H (mm) of the liquid refrigerant and axis of ordinate stands for the rate (kg/h) of flow which is introduced into the discharge pipe 203. Dashed lines indicate the flow rates of portions of the liquid refrigerant which are introduced through the oil-recovery holes 203a to 203e. An alternate long and short dash line rising to the right indicates the total flow rate of the liquid refrigerant introduced through the respective oil-recovery holes.
As the height H of the liquid refrigerant is enlarged, the number of the oil-recovery holes which exist in the liquid refrigerant 204 is enlarged. Since the rate of the flows which are introduced through the lower oil-recovery holes is enlarged by a quantity corresponding to the potential head of the liquid, the foregoing flow rate is enlarged as compared with a rate of the flows which are introduced through the upper oil-recovery holes. Therefore, the total flow rate of the liquid refrigerant is not enlarged in proportion to the height H of the liquid refrigerant. The total flow rate is enlarged with increasing speed. That is, as the level of the liquid refrigerant is raised, the quantity of the liquid refrigerant 204 which is sucked into the discharge pipe 203 and discharged from the accumulator is enlarged.
The flow rate of oil will now be described. A sawtooth solid line shown in FIG. 35 indicates a flow rate of refrigerating machine oil 205, which floats in the upper portion and which is introduced into the discharge pipe 203 through the oil-recovery hole. FIG. 36 is a diagram showing change in the flow rate of oil. The quantity of refrigerating machine oil is determined by the refrigerating and air-conditioning circuit which includes the accumulator. Since the diameter of each oil-recovery hole is usually determined to prevent excess accumulation of refrigerating machine oil in the accumulator, the quantity of refrigerating machine oil which is accumulated in the closed container 201 of the accumulator is not changed considerably. Therefore, one or two oil-recovery holes usually exist within the thickness h of refrigerating machine oil although the number varies depending on the intervals of the oil-recovery holes.
FIG. 36(a) shows a state in which refrigerating machine oil 205 is accumulated in a range including the two oil-recovery holes 203c and 203d. FIG. 36(b) shows a state in which refrigerating machine oil 205 is accumulated in a range including one oil-recovery hole 203d though the thickness h of refrigerating machine oil is the same as that in the case shown in (a). That is, the state shown in (a) or that shown in (b) can be realized depending upon the change in the height H of the liquid refrigerant. As a matter of course, the difference between the two states causes the flow rate of oil to be changed. Thus, the state shown in (a) is a state in which the flow rate of oil is larger than that in the state shown in (b). Therefore, even if the thickness h of refrigerating machine oil is constant, the flow rate of oil which is introduced into the discharge pipe 203 is somewhat changed when the height H of the liquid refrigerant is changed. In actual, the flow rate has the trend toward sawtooth change, as shown in FIG. 35.
An operation condition is considered in which the liquid refrigerant is mixed with the gas refrigerant which flows in the accumulator and the quantity of the liquid refrigerant in the liquid refrigerant is enlarged excessively. Moreover, refrigerating machine oil of the type which encounters the phase separation with the liquid refrigerant is used in the accumulator having the conventional structure (see FIGS. 33 and 34). In the foregoing state, the liquid refrigerant in a large quantity is introduced into the compressor because a large number of the oil-recovery holes exist. In the foregoing state, the compressor is brought to a state in which the liquid is compressed and thus abnormally high pressure is generated. Also the inside portion of the compressor encounters defective lubrication of the bearing portion because an oil-supply pump sucks the liquid refrigerant and thus supplies the liquid refrigerant to the bearing portions and sliding portions. As a result, the moving portions in the compressor encounter abnormal abrasion and seizure. Thus, the refrigerating and air-conditioning circuit encounters a defect in the cooling performance or in the operation. The foregoing state sometimes suffers from unsatisfactory reliability as compared with an arrangement in which refrigerating machine oil having solubility with the refrigerant is employed.
As can be understood from the description about the convention apparatus, the flow rate of the liquid refrigerant which is discharged from the accumulator included in the refrigerating and air-conditioning circuit is required to be not larger than a certain limit. On the other hand, a somewhat large flow rate of refrigerating machine oil is required to smoothly operate the compressor. The foregoing limits somewhat vary depending on the refrigerating and air-conditioning circuit which includes the accumulator.
To reduce the flow rate of the liquid refrigerant in the conventional structure shown in FIG. 33 or 34, the diameter of each oil-recovery hole is required to be reduced for example. However, the minimum diameter of the oil-recovery hole has a limit because a required flow rate of refrigerating machine oil which must be processed. Moreover, excessive reduction in the diameter is unfit for a mass production. What is worse, there is apprehension that clogging of foreign matter, such as dust, takes place if the diameter of the hole is too small. Therefore, the diameter must be larger than a certain value, for example, the diameter of the hole must be not smaller than about 1.5 mm. However, the foregoing diameter is too small to reduce the flow rate of the liquid refrigerant.
Moreover, another problem arises in the structures shown in FIG. 33 and 34 from a viewpoint of the flow rate characteristic of oil. That is, if the diameter of each oil-recovery hole is made to be a small diameter, the flow rate of the liquid refrigerant can be reduced. However, also the flow rate of oil is undesirably reduced. In this case, a required flow rate as refrigerating machine oil cannot be realized. In this case, oil in a large quantity is accumulated in the container of the accumulator, causing the quantity of oil in the compressor to be reduced.
As described above, the conventional accumulator is brought to a state in which the compressor sucks liquid refrigerant in a large quantity. Thus, the accumulator is brought to a state in which the liquid refrigerant is compressed, thus causing abnormally high pressure to be generated. Since the oil supply pump in the compressor sucks the liquid refrigerant and supplies the liquid refrigerant to the bearing portions and moving portions, the bearing portions suffer from insufficient lubrication. As a result, the mechanisms in the compressor can be broken, abnormal abrasion and seizure take place in the moving portion in the compressor.
As described above, the conventional accumulator has a problem in that the flow rate of each of the liquid refrigerant and refrigerating machine oil cannot appropriately be controlled if refrigerating machine oil having solubility with the refrigerant is employed or refrigerating machine oil having poor solubility with the refrigerant is employed. Thus, the reliability of the operation of the compressor has been unsatisfactory.